Drawing furnace



J. H. KNAPP DRAWING FURNACE Oct. 11, 1932.

- Filed Dec. 15. 1950 2 Sheets-Sheet 2 mm M Q w v,

Patented Oct. 11, .1932

UNITED STATES PATENT OFFICE JAMES H. KNAPP, 01 BEVERLY HILLS, CALIFORNIA, ASSI IIGNOR TO JAMES H. INAPP GOMPANY, OF LOSANGELIEB, CALIFORNIA, A. CORPORATION OF CALIFORNIA nmwme Bummer:

Application filed December 13, 1830. Serial No. 502,347.

My invention relates to furnaces, and particularly to furnaces which require an even, relatively low temperature. In the various heat treatments to which metals such as steel'and duralumin are subjected, it is frequently necessary to provide a furnace capable of producing a relatively low temperature and maintaining this temperature constant over a considerable period of time. 7 g

It is a corresponding purpose of my invention to provide a furnace adapted to subject articles to be treated to a temperature which is constant over a considerable interval of time, and which is relatively low, being from approximately 300 Fahrenheit to approximately 1200 F. v

The provision of a furnace operating to produce such a low, even temperature by conduction or radiation is diflicult, due to-the different rates at which heat is transmitted to the articles to be treated at such low temperatures and due to the fact that heating articles in a furnace by radiation begins to be practicable only at temperatures in excess of 1200? F. g

It is a purpose of my invention to provide a furnace which subjects articles to be treated to such a low, even temperature by convec- To accomplish this purpose it is necessary that heated gas should circulate and contact with the articles to be treated.

It is an object of my invention to provide a furnace of the class described which will effect the circulation of the heated gases into contact with the articles to be treated by the operation of the burner means of my invention. 1

It is a further object of my invention to provide a furnace with a burner means which directs the heated gases from the treating chamber to the combustion chamber in such amanner that these heated gases contact the articles to be treated in the treating chamber.

To accomplish the foregoing objects, and others, some of which will be made evident in the following description, I have illustrated one embodiment of my invention in the drawings in which, 1

Fig.1 is an elevational view of the furnace of my mvention.

Fig. 2 is a longitudinal section through a pair of burners of the furnace of my invention.

Fig. 3 is a lan view in section, taken as indicated b t e line 33 of Fig. 2, with a portion the furnace cut away on the horizontal plane passing through-the burners.

Fig. 4 is an end view, partially in section, taken as indicated by the line 44 of Fig. 3.

Referring to the drawings, which are for illustrative purposes only, the numeral 11 indicates the furnace of my invention which includes side walls 12 and 13 cooperating with ends 14 and 15, top 16, and bottom 17, to form an enclosure 18. These members may be formed of non-conductive heat resistin material which, if desired, may be covere with metal, as indicated by the numeral 19.

The enclosure 18 is divided by a horizontal bed 20 into an upper and a lower portion. As best illustrated in Figs. 3 and 4,

the ends of bed 20 contact the ends 14 and of the furnace 11, and the bed is supported by two longitudinal members 21 and 22 parallel to and a short distance on either side of the longitudinal axis of the bed 20. As best illustrated in Fig. 4, the longitudinal members 21 and 22 rest upon the bottom 17 of the furnace 11.

Supported upon the bed 20 at either side thereof are sectional members 23. Each of the sectional members 23 includes a body 24 with sides 25 extending erpendicular thereto. As illustrated in members 23 are supports upon the bed 20 so that the adjoining projecting sides 25 of the adjacent sectional members 23 engage each other and so that the bodies 24 of the sectional members 23 cooperate with the sides 12 and 13 to form a plurality of vertical passages 26.

Formed in the bed 20 upon the longitudinal axis thereof is a plurality of outlet openings 27 extending vertically through the bed 20 and communicating with a passage 28 between the longitudinal members 21 and Formed in the end 15 of the furnace 11 is i 3, the sectional is of a height substantially equal to the distance between the bed 20 and the inner surface of the top 16, and the width of the opening 29 is somewhat less than the distance between the inner surfaces of the sides 12 and 13. The entrance 29 is adapted'to be closed by a vertically slidable door 30 which may be attached to one end of a chain 31, to the other end of which is attached a counterweight 32. The door 30 may be elevated in any suitable manner, the means illustrated in Fig. 1 comprising a chain and pulley system 33. Extending from the end 15 on either side of the opening 29 are arms 34 to which are pivoted engagers 35 adapted to be manually operated to engage the outer surface of the door 30 when it is in its lowermost position to effect an airtight closure of the opening 29.

The bed 20, the ends 14 and 15, and the sectional members 23 cooperate to form a treating chamber 36 of the furnace of my invention. Combustion chambers 37 and 38 are defined by the bed 20, the side 12,

bottom 17 and the longitudinal member 21,

' and the bed 20, the side 13, the bottom 17 and the longitudinal member 22, respectively. Formed in each of the ends 14 and 15 is a slot 39 of a length somewhat. less than the distance between the inner surfaces of the sides 12 and 13, and of, a height equal to the height of the combustion chambers 37 and 38. Each of the combustion chambers 37 and 38 communicates with the slots 39 through a pair of openings 40. As illustrated in Fig. 3, each of the four openings 40 is substantially upon the longitudinal axis of one of the combustion chambers 37 or 38. Concentric with each of the openings 40 is a second cylindrical opening 41 formed in the ends 14 and 15 and extending from one of the slots 39 to the exterior of the furnace 11. The diameter of the openings 41 is substantially less than the diameter of the opening 40, for a purpose which will be later described.

Adapted to be secured in each of the open-d ings 41 is an extension 42 of a pipe 43. As illustrated in Fig. 2, the extension 42 comprises one part of a T, the other part 44 of which is provided with an opening 45 in its end through which a fuel pipe 46 extends. The pipe 43 and the fuel pipe 46 may be attached in airtight relationship with the The fuel pipes 46 are connected to a source of gas and air mixture supply (not-shown) and the pi es 43 are connected to a source of' compresse air supply such asia. blower 49.

The operation of my invention is as follows:

. The door 30 of the furnace 11, being in its closed position and retained in airtight engagement with the end 15 by means of the engagers 35, a mixture of combustible as and combustion-supporting gas is provi ed through the fuel pipe 46, discharged across the slots 39 and through theopenings 40 into the combustion chambers 37 and 38, and this mixture of gases isignited in the combustion chambers 37 and 38. Air under pressure is then provided by the blower 49 through the pipes43 and the passages 42, and is discharged across the slots 39 through the openings 40 of the combustion chambers 37 and 38. Due to the velocity with which the combustible and combustion-supporting gases are discharged from the fuel pipe 46, the flame of each burner will occupy in the combustion chamber substantially the position indicated by the dotted lines 50 of Fig. 2.

The air discharged through the extension 42 of the air pipe 43, forming an envelope around the flame 50 at each burner, is immediately heated and immediately tends to rise. This heated air, together with the gases of combustion, passes from each of the combustion chambers 37 and 38 upwardly through the passages 26 defined by the sectional members 23, as indicated by the arrows 51 of Figs. 2 and 4. The dischar e of the air from the extension 42, and the 'scharge of the combustible and combustion-supporting gases through the fuel pipe 46 across the slots 39 operate through the well known Venturi effect to draw gases from the slots 39 and project the same through the openings 40. This process operates to diminish the pressure within the slots 39 and within the passage 28 communicating therewith. This diminished pressure within the passage 28 causes the heated gases after their travel through the passages26 to be drawn downwardly towards the bed 20 and through the outlet openings 27 therein into the passage 28 and into the slots 39. It should thus be apparent that by discharging the combustion-supporting gas and the air across the slots 39 and through the openings 40, there is effected a circulation of the heated gases from the treating chamber 36 through the passage 28 and the slots 39 into the combustion chambers 37 and Inasmuch as it is necessary to provide for the escape of some of the gases of combustion, the embodiment of my invention illus trated includes two flues in each of the ends 14 and 15. As illustrated in Fig. 2, there are formed in the end 14 of the furnace 11 two vertical flues 53, each of which is substantially in the vertical plane of one of the combustlon chambers 37 and 38. Each of the flues 53 communicates with the treating chamber 36 through an opening 54 adjacent the bed 20.

The end 15 is likewise provided with two,

vertical flues 55 which communicate with the treating chamber 36 through openings 56 in that portion of the end 15 defining the opening 29 and adjacent the bed 20. The flues 53 and 55 may be connected in any suitable manner (not shown) to a discharge pipe.

In order to facilitate the control of the heat in the furnace of my invention, I provide a thermal control 57 extending downwardly through the top 16 of the furnace 11 and into the treating chamber 36. The thermal control 57 may be connected in any of the well known manners to a mixing chamber 58 illustrated in Fig. 1 to vary the proportion or amount of the mixture of the combustible and combustion supporting gases to maintain constant the temperature in the top of the treating chamber 36.

There may be provided also a thermometer 59 which is extended through the end 14 of the furnace 11 on that level in the treating chamber 38 at which the articles to be treated are placed. The thermometer 59, by giving an indication to the operator of the temperature adjacent the articles being treated, permits him to manipulate the valve 60 to vary the pressure of the air discharged from the air pipe 43, as indicated by the gage 61 of Fig. 1. I have found that a lower pressure on the air in the air pipe 43 is required to effect the desired circulation between the treating chamber 36 and the combustion chambers 37 and 38 at a high temperature than at a low temperature, due to the fact that the gases at the higher temperature are expanded to a greater extent. This greater expansion causes a higher pressure in the treating chamber 36 and thus at the higher temperature the recirculation is accomplished by the discharge of air from the air pipe 43 at a lesser velocity than at a lower temperature. To illustrate, I have found that a pressure in the air pipe 43 corresponding to two and onehalf inches of water in the gage 61 causes efi'ective recirculation when the temperature in the treating chamber 36 is 1200 F., while a pressure corresponding to ten inches of water is required for a temperature of 300 F.

Inasmuch as the bed 20 and the sectional members 23 may be formed of heat resistive material having a low conductivity, and inasmuch as the temperature secured is below 1200 F., which is the temperature .at which radiat on begins to be effective, it should be apparent that the furnace of my invention is adapted to heat articles placed in the treat ing chamber 36 almost entirely by convection. This renders it possible by maintaining constant' the ratio of air and combustible gassupplied to the furnace to maintain constant the temperature in the treating chamber 36.

It should also be apparent that by discharging the combustible and combustionsupportlng' gases across the slots 39 and through the openings 40, I have provided a means whereby the gases are caused to circulate from the treating chamber 36 to the combustion chambers 37'and 38. It is obvious that I have by my invention provided a furnace in wh'ch a recirculation of the heated gases is carried out so that the heated gases efi'ectively' contact the articles to be treated.

It should likewise be obvious that by such circulation of the heated gases there is achieved an even temperature throughout the treating chamber 36, so that articles therein are uniformly treated. I have found that such a uniform temperature may be achieved by the embod ment of my invention illustrated even though the treatingchamber be ten feet long, a. result not hitherto accomplished.

While that form of embodiment of my invention herein illustrated and described is fully capable of accomplishing all of the objects and purposes primarily stated, there are other embodiments of vmy invention which may likewise accomplish such purposes, and I therefore wish to be not restricted to the form of embodiment hereinbefore illustrated and described.

I claim as my invention:

1. In a furnace of the class described, the combination of: walls defining a treating chamber, a combustion chamber, and passages for discharging gas from said combustion chamber into said treating chamber; Walls defining a return passage, said Walls having openings therein; and burner means for injecting combustible and combustionsupporting gases through said openings into said combustion chamber.

2. In a furnace of the class described, the combination of walls defining a treating chamber; Walls defining a combustion chamber below said treating chamber; walls defining open ngs between said chambers for the passage of hot gas from said combustion chamber to said treating chamber; walls cooperating with Walls of said combustion chamber to form a return passage; and burner means for injecting combustible and combustion-supporting gases through said return passage into said combustion chamber to crculate gas around articles treated in said treating chamber and to said combustion chamber.

3. In a furnace of the class described, the combination of: walls defining a treating chamber; walls defining a combustion chamber below said treating chamber, said com bustion chamber being adapted to discharge hot gas into said treating chamber along the sides and intermediate the topand bottom thereof; walls cooperating with walls of said combustion chamber to form a return passage adjacent said combustion chamber, the wall between said return passage and said combustion chamber having an opening therein; and burner means for injecting combustible and combustion-supporting gases across said return passage and through said opening into said'combustion chamber.

4. In a furnace of the class described, the combination of: walls forming a treating chamber; walls forming a combustion chamher; burner means for introducing combustible and combustion-supporting gases into said combustion chamber; means for circulating gas from said combustion chamber around the articles treated in said treating chamber to said combustion chamber; and means for varying the velocity of said circulating gas. 5. In a furnace of the class described, the

from said combustion chamber into said treat- 7 combination of: walls defining a treating chamber; walls defining a combustion cham- 5 her below said treating chamber, said combustion chamber being adapted to discharge hot gas into said treating chamber along the sides' and intermediate the top and bottom thereof; walls cooperating with walls of said combustion chamber to form a return passage adjacent said combustion chamber, the wall between said return passage and said combustion chamber having an opening therein; burner means for injecting air and amixture of combustible and combustion-supporting gases across said return passage and through said opening into said combustion chamber to contact articles to be treated insaid treating chamber with hot gases; supply means for providing air to said burner means; and control means associated with said supply means for varying the pressure on the air provided to said burner means.

6. In a convection furnace of' the class described, the combination of: walls forming a treating chamber; walls forming therebelow I a combustion chamber which is entirely separate from but in communication with said treating chamber; hot gas producing means whereby hot gas is formed in said combustion chamber, said hot gas passing from said combustion chamber into said treating chamber; and means for returning said hot gas from said treating chamber to said combustion chamber, thus providing a closed circuit through which said hot gas passes.

7. In a convection furnace of the class described, the combination of: walls forming a treating chamber; walls forming therebelow a combustion chamber which is entirely separate from but in communication with saidv treating chamber; combustion producing means for producing combustion which takes place entirely in said combustion chamber, thus producing hot gas, said hot gas passing 

